The present invention relates generally to waste management, and particularly to a system for efficient, high capacity material recovery from a variety of sources including municipal solid waste, commercial waste, commingled waste, and demolition waste.
The recovery by one person of useable material from the refuse of another is as old as the practice of community waste collection and disposal. One persons's refuse has always had the potential to be another person's resource. The benefit of efficiently exploiting such wasted resources, however, grows as our population grows and our resources diminish.
Source separation of the recyclable or reusable items from the unusable refuse enhances our recovery of valuable resources, but requires extensive education of and effort by members of the public. In some areas, garbage collection services include curbside collection of pre-sorted recyclable materials, e.g., glass, metal, newspaper, and plastics, thereby avoiding any need to later separate such items. In other areas, the recyclables as a whole are separated from the unusable refuse, but are commingled and require later processing, i.e., for individual use as resources. Such curbside source separation and commingling of recyclable items as a method of material recovery is generally successful only in progressive, urban communities. In many large municipal areas, however, no source separation of any kind is practiced and reusable resources are mixed with unusable, undesirable, and contaminated waste. Extensive processing is required to recover the reusable resources. Such processing is the subject of the present invention.
As our natural resources diminish and our landfills expand to capacity, recovering valuable resources from our refuse and minimizing the volume of material committed to landfill burial become critical issues. This is particularly true in large cities where vast amounts of garbage are produced with little or no landfill capacity available, resulting in the undesirable transportation of garbage to the few remaining landfill sites. Also, many large cities have little hope of obtaining the cooperation of the local population in effective source separation.
Under early methods of material recovery, still practiced today, persons simply waited at a refuse dump site and picked through the garbage as it was delivered. For as long as there has been waste dumping sites, there have been persons sifting through the discarded material in search of recoverable or reusable items. As may be appreciated such methods of material recovery are neither organized nor efficient. For example, it is quite difficult, time consuming, or impossible to access items buried deep within the garbage pile. With transfer stations incorporated into waste collection systems, the opportunity to move refuse along a conveyor through a picking station permits recovery of some recyclables, but introduces a processing bottle-neck due to relatively low conveyor speed and reduced picking area material volume required to conduct such recovery. Adding large numbers of persons along expanded picking areas to improve system capacity only produces a labor intensive, and therefore inefficient, and large installation, and therefore expensive, solution.
According to a more recent material recovery approach, waste enters a processing system through an infeed conveyor and moves into an inclined trommel for size classification. The size classification merely separates the waste flow into large and small articles to aid in the subsequent manual separation of recoverable items from each of the resulting trommel output flows. Trommel output, i.e., unders and overs, moves into separate picking or sorting areas. As many as 150 people are then responsible for removing recoverables at the picking areas. Finally, the process ends with a ferrous removal station, e.g., large permanent magnet removing ferrous metals. The unrecovered material or unusable refuse is sent to a landfill. The basic system can be multiplied and operated in parallel, e.g., several trommels operating in parallel to provide the primary size classification. Unfortunately, this approach has proven to be expensive in relation to its capacity, typically processing only eight to ten tons of municipal solid waste per hour for a relatively large installation cost, e.g., on the order of eighty million dollars. Furthermore, trommels are expensive and relatively large items, requiring a relatively larger facility and associated greater real estate expense. Another deficiency of trommels as a size classification device is the undesirable breaking of glass articles. When a material recovery system breaks glass articles, the glass articles not only become unavailable for recycling, but also contaminate other portions of the material being processed. Finally, a trommel, basically a large inclined cylinder with material passing therethrough, tends to undesirably roll certain materials into balls which are essentially unrecoverable and tend to clog other portions of the material processing machinery if not removed. Thus, under this method of material recovery, the basic process of manual sorting is aided only by a primary size classification step and automated ferrous material removal, otherwise the recovery method is manual, massively labor intensive and requires a large facility.
According to other material recovery methods, an initial shredding step is executed, for example to release material from plastic garbage bags. Unfortunately, such a shredding process exposes the recyclable material to break-down and mixing with other material, e.g., breaking of glass, thereby reducing the potential yield available from the input refuse and degrading overall system efficiency. As may be appreciated, to the extent that a material recovery system can avoid degradation or breakage of input material, the resulting yield is increased by maintaining good separation throughout the system of whole items of recyclable material for manual or automatic separation.
Our municipal solid waste, commercial waste, commingled recyclable waste and demolition waste offer great opportunity for material recovery, but such material recovery must be efficient in separating re-usable from non-usable materials, and also in separating re-usable materials from one another. To the extent that such materials can be efficiently separated, the value or profit derived from such material recovery is enhanced. Furthermore, when a greater percentage of re-usable materials are taken, not only is less landfill capacity is needed but we also benefit by re-use of resources otherwise lost to landfill sites.
Accordingly, there exists significant need for high capacity, efficient material recovery systems. Such systems must be cost effective to meet the needs of large municipalities, with mandatory budget constraints, generating large volumes of municipal solid waste and other refuse material. The subject matter of the present invention provides such a solution to refuse material recovery.